The present invention relates to a rotary switch actuator and, more particularly to an actuator whose construction and operation has been modified to reduce the "bounce back" phenomena after the switch has been activated and released.
Mechanical/electrical rotary switches are well known in the art and have been used for a great variety of purposes. One function is to provide an electrical signal upon detecting the passage of an object such as a sheet of paper moving along a transport path. U.S. Pat. No. 5,042,790 discloses the use of a switch actuator which is positioned in a sheet transport path. The switch of the present invention can find utility in a sheet transport system of the type disclosed in this patent, whose contents are hereby incorporated by reference.
FIG. 1 illustrates a conventional prior art switch. A description of the switch and its operation is provided to identify and describe the cause of the "bounce back" phenomena which constitutes a problem for usage of this type of prior art switch. As shown in FIG. 1, the switch consists of a base substrate 2, which may be of a lightweight plastic construction, to which are mounted a horseshoe sensor 4 and a rotary switch assembly 6. Sensor 4 has a bifurcated or horseshoe configuration to establish upper and lower legs 8, 10, respectively. Upper leg 8 supports a light source such as a light emitting diode (LED) 12, where the lower leg 10 supports a light detector such as a photodiode 14. The diodes 12, 14 are aligned on a common sensing axis 16. Conventional wiring circuitry (not shown) supplies power to the LED 12 along connection 18, while output signals from photodiode 14 are sent to a system control circuit along connection 20. Switch 6, which may be made from a one piece molded plastic, comprises a hub 22 which is seated on a metal pivot post 24. Post 24 is rigidly connected to substrate 2. A curled hook segment 26 forms an extension of the hub and is used as the connection for one end of biasing spring 28. The other end of spring 28 is connected to a protrusion 30 which extends vertically upward from substrate 2. Switch 6 further comprises two arms 32, 34. Arm 32 is an arcuate shape and terminates in a tip 33 which projects an inclined edge surface 35 into the path of a paper sheet 36, moving in the direction of arrow 37. Arm 34 is generally oriented in the opposite direction and is positioned in its non-operative state so that the tip of arm 34 lies within the common sensing axis 16 between LED 12 and diode 14. In this position, the light from LED 12 is prevented from reaching diode 14; hence, there is no output signal on connection 20.
In operation, as paper sheet 36 moves in the direction of arrow 37, the leading edge encounters edge surface 35 of area 32 and begins to move arm 32 in a counterclockwise (CCW) direction. The movement is transmitted to all of the integral components of switch 6. Hub 22 is rotated about post 24 and the tip of arm 34 is rotated out of the position on sensing axis 16. Light from LED 12 illuminates diode 14, creating an output signal on connector 20. The signal, representing the arrival of a copy sheet, is sent to the system control and is used for timing and registration purposes. The rotational force imparted to switch 6 causes spring 28 to be extended, resulting the creation of stored energy which will return the switch to its original position when the trailing edge of sheet 36 exits the contact with edge surface 35 of arm 32. The "bounce back" phenomena is created when the spring energy is released and is a function of the way in which the bottom portion of hub 22 interfaces with the seating portion of frame 2. As shown in the exploded view in FIG. 2, two arcuate rectangular teeth like segments 40, 42, extend vertically upward from the substrate 2. The teeth are separated by 180.degree. and by a radial arc distance D. Hub member 22 has two, arcuate teeth-like segments 22A, 22B. When hub member 22 is fully seated, the body of the hub 22 is supported by the top surfaces of segments 40, 42, and teeth 22A, 22B are seated in the spaces between teeth 40, 42. The width of teeth 22A, 22B is less than distance D, thus providing the play required during switch rotation. During the CCW rotation of switch 6, hub 22 and teeth 22A, 22B rotate within the distance D until they come to a stop against the side of teeth 40, 42, respectively. Upon release of the energy stored in spring 28, switch 6 and hub 22 are rapidly rotated in a clockwise (CW) direction. The vertical edges of teeth 22A, 22B come to a hard stop against the vertical sides of teeth 40, 42. This results in a portion of the closing return force expended by spring 28 being translated back into the hub and throughout the structure of switch 6. This sometimes results in the tip of arm 34 "bouncing back" in a CCW direction sufficient to move the arm out of sensing axis 16, thus generating an incorrect (false) output signal from diode 14.
According to the present invention, this "bounce back" phenomena is practically eliminated by changing the seating configuration of the hub member of the switch so as to reduce the effect of the return force exerted by spring 28. More particularly, the present invention relates to a rotary switch actuator comprising:
an actuator arm pivotably mounted to a substrate for movement between a reset position and a switch activated position, a hub member mounted for rotation on a pivot member fixed in position on said substrate, the improvement wherein the bottom surface of said hub member has at least two inclined surface segments which mate with inclined surfaces protruding upward from the substrate.